The present invention relates to the extraction of non-surface active organic material from aqueous anionic surfactant solutions. Processes for the preparation of anionic detergents usually result in production of a mixture comprising water/anionic detergent/non-surface active organic material. It is desirable to remove the non-surface active organic material from the detergent product and this may be achieved in several ways, one of which is by the extraction thereof with suitable solvents.
One important class of anionic detergents includes those obtained by the sulphation or sulphonation or organic material. Examples include alkyl sulphates, alkyl sulphonates and alkenyl sulphonates. Such anionic detergents are suitably prepared by reacting C.sub.8 to C.sub.22 olefins or alcohols with sulphuric acid or sulphur trioxide or by reacting paraffins with sulphur dioxide and oxygen to form the corresponding sulphuric or sulphonic acids followed by neutralizing such acids with bases to form the corresponding salts which are anionic detergents. The principal products of such processes are aqueous solutions of sulphated or sulphonated organic matter. However, these products also contain organic material which is not surface active. Such non-surface active organic material may be unreacted starting material and/or may be formed during the process. Examples of this non-surface active organic material include C.sub.8 to C.sub.22 paraffins, olefins, and alcohols as well as various by-products such as polymers and sultones. This non-surface active organic material may also be described as unconverted organic matter.
In conventional practice, the above described non-surface active organic material is usually removed from the aqueous anionic detergent product by extraction with hydrocarbon solvents. The extraction usually takes place after neutralization since further amounts of non-surface active organic material may be formed during the neutralization reaction. One problem attributable to the use of hydrocarbons as sole extractants is that there is then a strong tendency toward formation of undesirable emulsions or gels. The emulsion formation may be avoided by carrying out the extraction in the presence of various oxygen-containing compounds such as low molecular weight alcohols, e.g. isopropyl alcohol (IPA), and ketones (see British Pat. No. 480,904; British Pat. No. 726,994). Thus insofar as gasoline/IPA extractions are concerned, the products are a gasoline/IPA/non-surface active organic material extract and a gasoline/IPA/water/ sulphated or sulphonated organic matter raffinate. The solvents may be separated, recovered and reused in further extractions. However, with the use of two solvents for extraction it is necessary to provide separate solvent recovery systems for each, a requirement which adds to the total capital and operating costs of a commercial extraction unit.